Fuse 27 blows when in neutral, Need help rerouting power to the backup lights

[Mbrooks420]

I'm thinking it is almost surely a rubbed through wire somewhere. I can't get my dealer cd to give me a schematic large enough to read, and that doesn't help. I don't even know if I have all the things to suspect. The fuse diagram isn't correct, as some of the things listed as being on the same circuit still work.

 

[Mbrooks420]

Well I pulled the front and rear seats, carpet, and lossened all the wiring harnesses running towards the rear. With a test light in the fuse panel, I can't get any variance in the light by moving harnesses. I disco'd the RAP, the DTR, another harness under the truck behind the transmission, and still no effect. It will blow fuses in drive, 2 and 1. In drive the test light gets a pulse, and in 2 and 1 it lights solid. This is even without the DTR sensor plugged in. Unless I am mistaken about what sensors I am unplugging. I am assuming the DTR is what the shift lever is hooked into. Is this a manual lever position switch? There is a large gray connector above this I couldn't get unhooked. I am going to work on that tomorrow. I haven't worked the harnesses loose behind where the rear seat was. I'm beat I've been at it since 4:30 and haven't made much headway.

 

[410Fortune]

have you messed with the digital transmission range sensor on the side oft hre trans itself? That wiring harness goes through a big black plug, then up the back of the trans into the engine harness and directly to the PCM....
I know that this harness is jsut the signals from to/from the transmission, and that your issue is a power distribution issue, but it wouldnt hurt to do the wiggle test down there.....

Man this is a very frustrating problem, I know how you feel. the pulse youwere getting in D on the test light, well that doesnt sound right either does it?

this is a dumb question too and its not always the smartes thing but have you tried a slightly larger fuse? hahaha I mean a dead shirt will blow anythig you stick in there, or melt your wires....

I think you are on the right path, keep going and you'll find it.

 

[Mbrooks420]

Yeah, I tried the larger fuse But only for a second to see if it would blow instantly, which it did. The pulse in D is wierd. It blinks once less than a second after selecting D, and then stays lit for consistant period of time of less than a second. Do you know what the large gray connector above the DTR is? I couldn't get that one unplugged. The DTR was full of road salt, but I cleaned it and put some dialectric grease in there.

 

[410Fortune]

Grey connector? when you say DTR you mean Digital Transmission Range Sensor?
That plug if you do mean DTR is the one that connects 3 02 sensors, the trans sensors, and the speed sensor tot he PCM harness.

OKay since the fuse ONLY blows when you use the shifter and not the other 5 circuits, it has got to be something connected to the shifting, DTR, or related wiring.

Same issue since you ditched the salt?

 

[Mbrooks420]

I am at my wits end. I disconnected every thing to the transmission, and all the modules behind the dash, except for the one that is behind the air bag(I couldn't reach it) and it still blows the fuse. I don't understand how it knows what gear it is in. It blew the fuse in reverse today, when it didn't before. A lit toggle switch wired directly from the battery to the backup lights is starting to look real good.

 

[Mbrooks420]

Well, problem solved. Fused switch from batt, directly to both reverse lights. Unfortunately I am throwing a CEl now Not sure where to start, but assume its connector related. I'm guessing it's something the trans uses for input since it seems the tranny is in limp mode.

 

[410Fortune]

oh man, what codes?

 

[Mbrooks420]

Not sure yet, hopefully will get them scanned tomorrow, with the reinspection, and emmisions.

 

[V8BoatBuilder]

FYI, up here in MA, they'll flunk you right away if your CEL is on, no matter what the code is.

 

[Mbrooks420]

That won't be a problem here. With any luck I'll get it fixed tonight though.

 

[Mbrooks420]

Well I went ahead and bought a code reader. It is reading code 0720 output speed sensor malfunction. I assume Fords name for this sensor is the Vehicle Speed Sensor? I didn't think that was part of the transmission, but the axle.

 

[410Fortune]

in a 98 you will have two, one in the trans tailshaft and one in the rear axle.
I am not exactly sure but the stator in the 8.8 is used for ABS, while the one in the trans is for the PCM and speedo....

Wow this has been a nightmare

 

[Mbrooks420]

Hmmmm, my speedo is acting correctly. I have a feeling this is going to be about as cut and dry as the fuse problem It would make sence that the PCM isn't getting the speed signal since the transmission is working in limp mode.

 

[Nate1]

At this point, a multimeter is your best friend....

I don't think you'll be able to solve with without one... just systematically (with the battery/truck off) check the resistance of each lead that you can possibly check of any sensor/component tied to fuse 27.

 

[V8BoatBuilder]

Hmmmm, my speedo is acting correctly. I have a feeling this is going to be about as cut and dry as the fuse problem It would make sence that the PCM isn't getting the speed signal since the transmission is working in limp mode.

Your speedo data is pulled from the rear axle ABS sensor. The OSS is for your transmission... I would go back and check your transmission harness.

Have you dropped the transmission pan? There are a lot of wires submerged in there, something may have been pinched or some insulation became worn down.

 

[Mbrooks420]

I haven't dropped the pan. I tried to reconnect the trans harness, but I will redisconect it, and clean it out, and make sure it goes back together tightly, and see what happens.